Proportioner

ABSTRACT

In a proportioner for proportioning a fluid flow (φ) from an input side of a first proportioning element ( 10 ) to an output side of a second proportioning element ( 10 ), the first and second proportioning elements comprise a membrane ( 12 ) provided with at least one opening ( 16 ) acting as a flow resistor for a medium to be proportioned, and a pressure sensor ( 14 ) integrated in the membrane ( 12 ) and used for detecting a pressure difference between the input side and the output side of the proportioning element ( 10 ). The proportioner comprises a pressure transducer for input-side application of a pressure to the medium to be proportioned. The first and the second proportioning element ( 10 ) are arranged in succession so as to permit, on the basis of the pressure drop across the membranes ( 12 ) of the two proportioning elements ( 10 ), the detection of clogging or blocking of the respective flow resistor provided in these membranes ( 12 ).

CROSS REFERENCE TO RELATED APPLICATIONS

“not applicable”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OF DEVELOPMENT

“not applicable”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a proportioner for proportioning afluid flow, when medicaments are to be dosed in the field of medicalengineering.

2. Description of Prior Art induding information disclosed under 37 CFR1.97 and 1.98

In the field of medical engineering, proportioners are known, whichcomprise flow resistors whose flow rate depends on the pressure withwhich the medium to be proportioned is acted upon before the flowresistor, when seen in the direction of flow. For detecting the pressuredifference, two different pressure sensors are normally used, thepressure sensors being arranged before and after the flow resistor, whenseen in the direction of flow.

Known flow resistors consist e.g. of glass capillaries or microchannelsin a capillary form. A disadvantage of such known proportioners is thatthey have a complicated structural design due to the fact that a flowresistor and two different pressure sensors, which arranged before andafter the flow resistor when seen in the direction of flow, arerequired.

In the Patent Abstracts of Japan, P 1828, Nov. 18, 1994, Vol. 18, No.609, a means for measuring a flow rate is described, in the case ofwhich an elastic plate with an opening is arranged in a passage or in atube through which fluid flows. Furthermore, means for detecting thedeflection of the elastic plate are provided in the elastic plate.

DE 195 29 396 A1 discloses a measuring device for measuring the flowrate of a medium flowing in a flow cross-section, in the case of which aplate acted upon by the medium is flexible due to cuts formed therein,the plate having provided thereon strain gauges for detecting adeflection of the plate.

DE 42 23 067 C2 describes a micromechanical flow restrictor which isimplemented in a multilayer structure. This flow restrictor is adaptedto be used in combination with a micromechanical valve formicromechanical proportioners.

DE 19 43 021 AS teaches that a means is used for measuring the flowthrough a tube according to the differential pressure flow meteringmethod in the case of which an elastic deformation of a componentdepending on the pressure to be measured is converted into an electricsignal. The strain gauges used for detecting the elastic deformation aredirectly attached to an elastic orifice plate which is arranged in thetube through which the fluid flows.

BRIEF SUMMARY OF THE INVENTION

It is the object of the present invention to provide a proportioner witha simple structural design, which permits exact proportioning of amedium to be proportioned and which also offers the possibility ofdetecting clogging of the proportioner.

In accordance with a first aspect of the invention, this object isachieved by a proportioner for proportioning a fluid flow from an inputside of a first proportioning element to an output side of a secondproportioning element, said first and second proportioning elementscomprising a membrane provided with at least one opening acting as aflow resistor for a medium to be proportioned, and a pressure sensorintegrated in the membrane and used for detecting a pressure differencebetween the input side and the output side of the proportioning element.The proportioner comprises a pressure transducer for input-sideapplication of a pressure to the medium to be proportioned. The firstand the second proportioning element are arranged in succession so as topermit, on the basis of the pressure drop across the membranes of thetwo proportioning elements, the detection of clogging or blocking of therespective flow resistor provided in said membranes.

In accordance with a second aspect, the present invention provides aproportioner for proportioning a fluid flow from an input side of aproportioning element to an output side thereof, the propotioningelement comprising a membrane provided with at least one opening actingas a flow resistor for a medium to be proportioned and a pressure sensorintegrated in the membrane and used for detecting a pressure differencebetween the input side and the output side of the proportioning element.A passive flow resistor is arranged before or after the proportioningelement when seen in the direction of flow, wherein the proportionercomprises a when seen in the direction of flow, wherein the proportionercomprises a pressure transducer for input-side application of a pressureto the medium to be proportioned, and wherein detection of clogging orblocking of the flow resistor provided in the membrane is possible onthe basis of the pressure drop across the membrane of the proportioningelement.

The proportioning elements preferably consists of a semiconductor chipprovided with a semiconductor membrane, the pressure sensor beingdefined by piezoresistive resistors arranged on or in the membrane. Inaddition, the semiconductor chip, which can consist e.g. of silicon, haspreferably integrated therein a temperature sensor.

Preferably, a control device is provided for controlling thecontrollable pressure transducer in dependence upon the pressuredifference detected by means of the pressure sensor and/or thetemperature detected by means of the temperature sensor.

An alarm signalling device can be provided for outputting an alarm ifflow passages arranged before and/or after the membrane have a leak orare clogged or if the at least one opening of the membrane is clogged;such malfunctions can be recognized on the basis of the pressuredifference detected by the pressure sensor.

In comparison with known proportioners, the proportioner according tothe present invention is advantageous insofar as the pressure differenceis determined directly by means of a sensor instead of being determinedby two pressure measurements relative to the atmosphere, the results ofthe two measurements being then subtracted from one another.Furthermore, the flow resistor, i.e. the restriction, according to thepresent invention is integrated directly in the pressure sensor. Hence,only a single chip is required, the chip fulfilling both the function ofdifferential pressure measurement and the function of the flow resistor,i.e. the flow restricting function.

Further developments of the present invention are disclosed in thedependent claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following, a preferred embodiment of the present invention willbe explained in detail, part of the explanation referring to the figuresenclosed, in which:

FIG. 1 shows a schematic cross-sectional view of a proportioning elementfor the proportioner according to the present invention;

FIG. 2 shows a schematic view of a first embodiment of the invention;and

FIG. 3 shows a schematic view of a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As can be seen in FIG. 1, a proportioning chip, which is implemented asa piezoresistive pressure sensor with one or a plurality of holes in thepressure sensor membrane, serves as a proportioning in the preferredembodiment of the present invention, the holes in the pressure sensormembrane serving as a flow resistor having a defined flow resistance.

In FIG. 1, the proportioning chip, which is preferably defined by asemiconductor chip consisting e.g. of silicon, is designated generallyby reference numeral 10. A membrane 12 is formed in the chip e.g. byconventional etching techniques. In the preferred embodiment, themembrane has arranged thereon four resistors 14, which are arranged in aWheatstone bridge circuit and only two of which can be seen in FIG. 1.Furthermore, the membrane has provided therein at least one opening 16which serves as a flow resistor having a defined flow resistance. Theopening 16 can be formed in the membrane 12 e.g. by means ofconventional dry etching techniques.

In the embodiment shown in FIG. 1, an overpressure is applied to themembrane 12 on the left-hand side thereof. This results in thedeformation of the membrane which is shown in FIG. 1 and which can bedetected by means of the piezoresistive resistors 14. This deformationis a measure of the overpressure applied to the membrane 12.

When such an overpressure is being applied, the medium to beproportioned, i.e. a liquid or a gas, will flow through the hole 16 oralternatively the holes, if a plurality of holes is provided in themembrane 12. As it has been described, the membrane 12 is deflected dueto the pressure drop, whereby the pressure difference across the flowresistor, which exists between the input side on the left-hand side ofFIG. 1 and the output side on the right-hand side of FIG. 1, can bedetected directly.

The flow φ, which is indicated by the arrow in FIG. 1 and which flowsthrough the flow resistor, is a function of the pressure applied to theflow resistor.

If the flow resistor, i.e. the flow restriction, consists of a holewhose diameter is much smaller than the length thereof, the relationshipbetween flow and pressure will be linear. The flow rate is primarilylimited by a laminar friction. A flow law is obtained, which is similarto the Hagen-Poiseuille law. If the diameter of the opening 16 is muchlarger than the length of the opening, the flow conditions are similarto a friction-free flow out of an orifice, a flow dependence, whichdepends on the square root of the pressure difference across the flowresistor, being obtained in this case according to the Torricelli law.

In any case, the flow through the flow restriction is a monotonouslyincreasing function of the pressure drop across the flow restriction.Hence, a calibration is possible, the flow being determinable bymeasuring the pressure drop. The chip is therefore suitable forproportioning fluids, i.e. gases and liquids.

Every flow medium has its viscosity n(T), which depends on thetemperature, as a characteristic property. It follows that, especiallyin cases where a quantitative flow measurement is to be carried out, itwill be advantageous to integrate a temperature sensor on the chip. Thetemperature of the flow medium can then be detected by the sensor.Furthermore, it will be advantageous to know the function n(T) for aspecific flow medium. On the basis of the temperature detected and thefunction n(T), a controllable pressure transducer of a proportioner canthen be readjusted in response to a temperature variation so as to keepthe flow constant at a specified proportioning rate.

Proportioners operating according to the overpressure principle, forwhich the proportioning element according to the present invention canbe used, frequently comprise pressure transducers for producing anoverpressure. For proportioning purposes according to the overpressureprinciple, an overpressure in the order of 50 kPa is frequently used. Itis apparent that, when an overpressure in this order of magnitude isused, the pressure sensor should be adapted to this pressure.

If chemically agressive flow media are to be proportioned, areas of thesemiconductor chip which are exposed to the medium to be proportionedcan be provided with a passivation layer. In particular, it will beadvantageous to provide conductor paths on the front of the pressuresensor with a passivation of this kind.

In the following, exemplary orders of magnitude for the proportioningelement according to the present invention will be indicated in brief.The lateral dimensions of the pressure sensor membrane 12 preferablyrange from 2×2 mm² to 5×5 mm². The membrane thickness preferably rangesfrom 20 μm to 60 μm. The diameter of the opening 16 can e.g. range from10 μm to 100 μm. As has been explained above, a plurality of openings 16can be arranged in the membrane 12.

In the following, it will be described how an alarm signalling devicecan output an alarm on the basis of the signals outputted by thepressure sensor 14, if malfunctions, e.g. leaks or clogging, occur in aproportioner including the proportioning element according to thepresent invention. Such an alarm can be a live-safing function, e.g. inthe field of the medicament dosing.

A first malfunction which may occur is a failure of the pressuretransducer. If the pressure transducer fails, no fluid or only a verysmall amount of fluid will flow through the opening of the membrane. Theflow of a small amount of fluid can e.g. be caused by a hydrostaticpressure resulting from the difference in height between a reservoircontaining the medium and an output of the proportioner. Hence, there isno or only a very low pressure drop across the pressure sensor, an alarmfunction being in this case triggered by an alarm signalling devicewhich can be integrated e.g. in a control device of the proportioner.

Other malfunctions can be caused by leaks in flow passages before andafter the flow resistor when seen in the direction of flow. If a leak islocated before the flow resistor, i.e. on the high-pressure side, theresultant change of flow will also be detected by the differentialpressure measurement, since the amount of fluid flowing through theproportioning chip is now smaller. A leak after the flow resistor, whenseen in the direction of flow, i.e. on the low-pressure side, is,however, much less likely. Such a leak cannot be detected by theproportioning chip. As a safety measure, the proportioning chip shouldtherefore be arranged at the smallest possible distance from theproportioning outlet of the proportioner, e.g. at the cannula, and itshould be attached by means of the least possible number of connectorsof the best possible quality.

A further malfunction can be caused by clogging of the flow passagebefore or after the flow resistor. In the case of medicament dosing, forexample, a cannula attached to the patient will often clog after sometime so that the proportioning function is no longer guaranteed. If theflow passage clogs before or after the flow resistor, e.g. in a filteror in the cannula, a flow of fluid will no longer take place so that apressure drop across the pressure sensor will no longer exist. An alarmfunction can therfore be triggered in this case.

It is also possible that the flow resistor of the proportioning chipitself clogs, the flow resistor being formed by the opening in themembrane. The whole pressure drop then exists across the proportioningchip, i.e. across the membrane. Normally, the pressure drop across theproportioning chip is, however, much larger than the pressure dropacross the rest of the proportioner, e.g. hoses, connectors, filters orcannulas of the proportioner. Hence, it will not be possible todifferentiate between the small, measured increase in pressure occurringwhen the restriction clogs and the increase in pressure resulting from atemperature increase of the flow medium in the case of liquids, or afrom a temperature decrease of the flow medium in the case of gases. Inthe case of liquids the viscosity decreases as the temperatureincreases, which has the effect that the flow and, consequently, thepressure rise increases, whereas in the case of gases the viscositydecreases as the temperature decreases. If triggering of an alarmfunction is also desired in such cases of clogging of the flow resistorin the membrane, additional measures are required.

A first measure is that two proportioning chips of the above-describedkind are arranged in succession. During normal operation, approximatelyhalf the proportioning pressure drop then exists across each of the twoidentical chips. If the opening of one of the two proportioning chipsclogs, the whole pressure drop will exist across this proportioningchip, whereas no pressure drop will exist across the other chip. Theclogging of the flow resistor, i.e. of the opening, can therefore bemeasured reliably. By means of such an arrangement of two successiveproportioning chips, it is also possible to measure a partial blockingof a flow resistor, since the ratio of the two pressures then shiftsaway from 1:1. A disadvantage is, however, the higher expenditure, sincetwo chips are required, and since the expenditure for system controlwill be higher as well.

A further possibility of recognizing clogging in a flow resistor isoffered when a proportioning chip and a passive flow resistor arearranged in succession. When a passive flow resistor is arranged inseries with the proportioning chip, before or after the proportioningchip when seen in the direction of flow, the flow resistance in the caseof nominal flow being equal to that of the proportioning chip, half theproportioning pressure drop will exist across the proportioning chip andthe other half of the proportioning pressure drop will exist across thepassive flow resistor during normal operation. If the flow resistor ofthe proportioning chip is clogged, the pressure drop across the flowresistor will double, and this will be recognized by the system controlas an alarm case, provided that the pressure drop does not fall withinthe pressure range given in the case of pressure control due to thechange of viscosity caused by a temperature variation. If this pressureincrease to a value that is twice as high does not suffice, it will alsobe possible to increase the ratio of the flow resistances of the passiveflow resistor and of the flow resistor of the proportioning chip.Elements which are suitable to be used as passive flow resistors aree.g. glass capillaries, microchannels or holes etched in silicon.

It follows that the present invention provides proportioning elements aswell as proportioners making use of these elements in the case of whichthe pressure difference is determined directly by a sensor, instead ofbeing determined by two pressure measurements relative to theatmosphere, the results of these two pressure measurements being thensubtracted from one another. In addition, only a single chip is requiredaccording to the present invention, the chip fulfilling both thefunction of differential pressure measurement and the function of flowrestriction, since the restriction is directly integrated in thepressure sensor.

FIG. 2 shows a schematic view of a first embodiment of a proportionerfor proportioning a fluid flow from an input side of a firstproportioning element 10′ to an output side of a second proportioningelement 10″, wherein each of the proportioning elements has a structuredescribed above referring to FIG. 1 and including a pressure sensor 12.In the embodiment shown in FIG. 2, a temperature sensor 20 is providedfor detecting the temperature of the medium 22 to be proportioned. Inaddition, a pressure transducer 24 for input-side application of thepressure to the medium to be proportioned is provided. A control device26 is connected to the pressure sensor 12, the temperature sensor 20 andthe pressure transducer 24.

In FIG. 3 a second embodiment of an inventive proportioner is shown. Thesecond embodiment comprises the same features as the first embodimentexcept for the fact that the first proportioner element 10′ is replacedby a passive flow resistor 28.

What is claimed is:
 1. A proportioner for proportioning a fluid flowfrom an input side of a first proportioning element to an output side ofa second proportioning element, comprising: said first and secondproportioning elements, a proportioning element comprising: a membraneprovided with at least one opening acting as a flow resistor for amedium to be proportioned, and a pressure sensor integrated with themembrane and used for detecting a pressure difference between the inputside and the output side of each proportioning element, a pressuretransducer for input side application of pressure to the medium to beproportioned, wherein the first and the second proportioning elementsare arranged in succession so as to permit, based on a pressure dropacross the membranes of the first and second proportioning elements,detection of either clogging or blocking of the respective openingprovided in said membranes.
 2. A proportioner according to claim 1, saidproportioning element further comprising: a temperature sensor fordetecting the temperature of the medium to be proportioned, saidtemperature sensor located on said proportioning element.
 3. Aproportioner according to claim 2, wherein the proportioning element isimplemented as a semiconductor chip, the membrane being a semiconductormembrane.
 4. A proportioner according to claim 3, wherein the pressuresensor is defined by piezoresistive resistors arranged either on or inthe membrane.
 5. A proportioner according to claim 3, wherein thetemperature sensor is integrated on the semiconductor chip.
 6. Aproportioner according to claim 3, wherein areas of the semiconductorchip which are exposed to the medium to be proportioned are passivated.7. A proportioner according to claim 1, wherein the pressure transduceris a controllable pressure transducer, said proportioner furtherincluding a control device for controlling the controllable pressuretransducer in dependence upon at least one of: the pressure differencedetected by means of the pressure sensor; and the temperature detectedby means of the temperature sensor.
 8. A proportioner according to claim1, further comprising an alarm-signaling device for outputting an alarmin the event of any of: if flow passages before the membrane either havea leak or are clogged; if flow passages after the membrane either have aleak or are clogged; and if the opening of the membrane is clogged.
 9. Aproportioner according to claim 1, wherein the proportioning elementsare arranged in the proportioner close to a proportioning outlet of saidproportioner.
 10. A proportioner for proportioning a fluid flow from aninput side of a proportioning element to an output side thereof,comprising: said proportioning element, wherein said proportioningelement comprises: a membrane provided with at least one opening actingas a flow resistor for a medium to be proportioned; and a pressuresensor integrated with the membrane and used for detecting a pressuredifference between the input side and the output side of theproportioning element; a passive flow resistor arranged either before orafter the proportioning element when seen in the direction of flow; anda pressure transducer for input-side application of pressure to a mediumto be proportioned, wherein detection of either clogging or blocking ofthe opening provided in said membrane is possible based on a pressuredrop across the membrane of the proportioning element.
 11. Aproportioner according to claim 10, the proportioning element furthercomprising: a temperature sensor for detecting temperature of the mediumto be proportioned.
 12. A proportioner according to claim 10, whereinthe proportioning element is implemented as a semiconductor chip, themembrane being a semiconductor membrane.
 13. A proportioner according toclaim 12, wherein the pressure sensor of the proportioning element isdefined by piezoresistive resistors arranged on or in the membrane. 14.A proportioner according to claim 12, wherein the temperature sensor ofthe respective proportioning elements is integrated on the semiconductorchip.
 15. A proportioner according to claim 12, wherein areas of thesemiconductor chip exposed to the medium to be proportioned arepassivated.
 16. A proportioner according to claim 10, wherein thepressure transducer is a controllable pressure transducer, saidproportioner further including a control device for controlling thecontrollable pressure transducer in dependence upon at least one of: apressure difference detected by means of the pressure sensor; and atemperature detected by means of the temperature sensor.
 17. Aproportioner according to claim 10, further comprising: an alarmsignaling device for outputting an alarm in the event of any of: if flowpassages before the membrane either have a leak or are clogged; if flowpassages after the membrane either have a leak or are clogged; and ifthe opening of the membrane is clogged.
 18. A proportioner according toclaim 10, wherein the proportioning element is arranged in aproportioner close to a proportioning outlet of said proportioner.